I just upgraded from an older version of the IDE which worked just fine compiling programs with the SHT21 LibHumidity library. In the Arduino 1.6.0 IDE, any programs that use this library will not compile. The error given is that the file wiring.h was not found, which is being included in the LibHumidity.cpp library. Editing the LibHumidity.cpp file and remming out this include solves the problem and SHT21 programs will compile without errors. Just thought I would pass on this info in case others are having this issue and hope that it will be fixed in the library download.